The present invention relates to a semiconductor light emitting device and an apparatus using the same, and more particularly to a semiconductor light emitting device in which a light emitting element such as a semiconductor laser or a light emitting diode is used, the assemblage and adjustment are simple or easy and a collimated beam having a small beam diameter can be generated.
In the conventional semiconductor light emitting device, as shown in FIG. 5, a light emitting element 1 is disposed at a focal point or position of one lens 2 to produce a collimated beam 4. The prior art relevant to this type of device includes the Institute of Electronics, Information and Communication Engineers of Japan, Omnibus National Convention, No. 2452, Spring 1987 and the Institute of Electronics, Information and Communication Engineers of Japan, National Convention on Semiconductors and Materials Departments, No. 319, Autumn 1987. In the conventional device shown in FIG. 5, the beam diameter d of the collimated beam 4 is EQU d=2.multidot.f.multidot.tan .theta. (1)
provided that the divergence angle of the light emitted by the light emitting element 1 is 2.theta. and the focal lens of the length 2 is f. In general, the collimated beam has a higher utility value the narrower it is. Especially in the case where the collimated beam is used in an optical fiber communication system, the beam diameter not larger than 1 mm is frequently required.
However, if the beam diameter is made small, it is apparent from the equation (1) that the focal length of the lens 2 or a distance between the light emitting element 1 and the lens 2 required becomes small so that the positioning (or location) and fixing of the light emitting element 1 and the lens 2 becomes difficult. For example, in the case where a semiconductor laser having a wavelength of 1.54 .mu.m is used as the light emitting element 1 and a small or minute spherical lens made of TaF.sub.3 glass is used as the lens 2, a focal length f equal to about 0.6 mm is required to produce a collimated beam having a beam diameter of 1 mm when the half angle .theta. of divergence of the emitted light is typically 40.degree..
On the other hand, the radius r and focal length f of a spherical lens have therebetween a relation of EQU r=2.multidot.f.multidot.(n-1)/n (2)
where n is the refractive index of the lens. By introducing f=0.6 mm and n=1.78 (the refractive index of TaF3 glass at the wavelength 1.54 .mu.m) into the equation (2), we obtain r.perspectiveto.0.53 mm. In the case of the spherical lens, the focal length f is a distance from the focal point to the center of the spherical lens. Accordingly, a distance l from the focal point to the end surface of the spherical lens is expressed by EQU l=f-r=(2-n).multidot.f/n (3)
by virtue of the equation (2). By introducing f=0.6 mm and n=1.78 into the equation (3), we obtain l.perspectiveto.0.07 mm.
To fix the semiconductor laser 1 and the spherical lens 2 with their optical axes aligned with each other is a very difficult task. Also, there is a high possibility that the lens 2 or an operating jig will touch the semiconductor laser 1 during the fixing work, thereby damaging the semiconductor laser 1. Further, a tolerance for positional deviation of parts which may take place in fixing the parts by means of adhesive or solder becomes small.